The character is first introduced in Jack Pumpkinhead of Oz, in which he's a somewhat pivotal character, but not a particularly major one. Jack and Peter Brown find the Jinn's dinner bell, which will summon a slave with a tray of food whenever someone rings it. When his companions are swallowed up by a magic sack, Jack gets the idea to grab the slave as he dematerializes, and ends up at the red glass castle. In this book, the castle is described as being "on the edge of a green glass sea," with a beach that "was a gleaming stretch of glass splinters." The Jinn himself turns out to be a rather odd fellow, who laughs uncontrollably at the slightest provocation, but also has a terrible temper when disappointed. John R. Neill's illustration of the character makes him look very creepy.
The Jinn receives a brief mention in Pirates, but it's Purple Prince that really elevates him to the status of a major character, and also softens him considerably. He still has his exaggerated moods and a tendency to joke about everything, but he comes across as somewhat more of an overgrown spoiled child than the unpredictably bizarre character he had been in Jack Pumpkinhead. The beach on which his castle sits is no longer made up of glass splinters (my personal explanation is that the glass was the result of a magical experiment gone awry), and is clearly identified as being located in Ev. In this book, Randy and Kabumpo visit Jinnicky to seek his help in restoring the royal family of Pumperdink. He takes a liking to Randy immediately, and while he's initially bothered by Kabumpo's haughty manner, the two of them also become friends during their journey. It's also in this book that Jinnicky first meets Ozma and the Wizard of Oz, and becomes an ally of the former and a professional rival of the latter. He shows up at a party held by Ozma in Wishing Horse, and is one of the people sent to the bottom of Lightning Lake by King Skamperoo's spell. Neill also started drawing him with a much more pleasant appearance.
By the time of Silver Princess, Jinnicky is clearly a good guy. Well, at least that seems to be how Thompson wants her readers to think of him, but the actions in this book don't entirely support that, especially when examined from a modern viewpoint. Gludwig, the manager of Jinnicky's ruby mines, leads a rebellion of the Jinn's black slaves, getting Jinnicky himself out of the way by throwing him into the ocean. When the Jinn regains his throne, with the aid of Randy and Kabumpo, it's reported that his miners "were only too willing to return to the mines, for with Jinnicky back in power their hours were short, their wages high and each miner had his own cozy cottage and garden." Then why did they want to rebel in the first place? While a compelling plot (if one that starts rather late in the story), it comes uncomfortably close to a popular racist myth of the time (appearing, from what I've heard, in the film Birth of a Nation), which is that the American black slaves were HAPPY doing difficult manual labor for no pay, until outside agitators stirred them up.
When Jinnicky and his court return in Yankee, Thompson's last book to feature the Wizard of Ev, his staff is still largely black, but with no hint of their being slaves. Ginger, the boy who responds to the magic dinner bell, is now simply a bellboy. The Jinn also mentions that his country now has a "share and share alike" economy, with everyone sharing equally in the profits from the ruby mines (although Jinnicky himself still gets the most). Kind of odd that an American children's book from the Cold War era would present a communist system in a positive light, but I guess Thompson didn't roll with the punches in EVERY respect.
Despite his slave-keeping, Jinnicky is a favorite of many Oz fans (as he was of Thompson himself), and shows up from time to time in fan-written works. I understand that there was a book from the forties with the Jinn as the title character, but it's difficult to find, and I haven't read it (although I'd definitely like to). I have, however, read Robert Pattrick's origin story for Jinnicky, which appears in an Oziana from the seventies. This tale explains how, under the tutelage of Glinda, the jug-maker and minor magician Juggins becomes the great Wizard of Ev.
Well, that's it for now. Tomorrow, we'll look at one of Jinnicky's own creations.